1. Field of the Invention
The present invention relates to apparatus and methods for making reclosable bags, and, more particularly, concerns a vertical form, fill and seal machine and method for making reclosable, product-filled bags.
2. Prior Art
Vertical form, fill and seal machines for making reclosable bags have been described, for example, in U.S. Pat. Nos. 4,709,533, 4,874,257, and 4,894,975. In particular, U.S. Pat. No. 4,709,533 describes a method and apparatus for making reclosable bags having a fin seal wherein a bag forming film is fed downwardly and wrapped around a spout and the edges of the film are brought together and pressed between pressing rollers to guide the edges together so that an outer fin seal can be formed by heated sealing bars. Interlocked zipper members, each attached to a respective web, form a zipper assembly which is fed between the film layers adjacent the outer edge between the pressing rollers and the spout and the zipper webs are sealed to the inner surface of the bag film by the heated sealing bars. The thus formed and sealed tube is filled with product through the spout and cross-seals and cross-cutters complete the individual bags. The fin seal is located outwardly of the reclosable zipper so as to serve as a tamper proof seal which not only protects the contents of the bag from the ingress of foreign materials and contamination but also prevents tampering with or premature inadvertent opening of the bag.
Above-mentioned U.S. Pat. No. 4,874,257 describes a vertical form, fill and seal apparatus and bag making process wherein a U-shaped zipper tape is heat sealed to the edges of a bag forming film while the film is wrapped around a cylindrical mandrel. Similarly, above-mentioned U.S. Pat. No. 4,894,975 discloses a vertical form, fill and seal apparatus which produces reclosable bags by feeding a thin thermoplastic film about a filling tube with the edges of the film brought together and joined by a zipper strip having reclosable pressure interlocking members. The zipper strip is heat sealed to the film and includes a web between the pressure interlocking members which web provides a tamper evident juncture between the edges of the film since the web must be severed for access to the interior of the bag.
Although the above described patents provide examples of vertical form, fill and seal apparatus and methods for forming reclosable bags, there is a need for an improved vertical form, fill and seal machine and method which not only forms reclosable, product-filled bags having a safety seal exterior to the reclosable seal but also which produces durable, substantially airtight bags at high speeds and which facilitates the production of different size bags and readily accommodates the addition of different amounts of product.